It is one of the important things for the ultrasonic inspection that a direction of propagation of ultrasonic wave signals from a transducer to a medium, which is usually a material to be tested for internal defects, is set freely. For the purpose, various ideas have been proposed. Mori et al introduced ultrasonic inspection where it is possible to set freely the direction of propagation of ultrasonic wave signals in "Phased Array Type Ultrasonic Inspection Method and Equipment" in a magazine, Journal of Institute of Japan Mechanical Engineers, Vol. 87, No. 793, Dec., 1984. In the conventional system, a plurality of elements of a transducer, namely a plurality of ultrasonic wave signal sending means and/or receiving means, are placed adjacently each other. This is called a phased arrayed transducer. Each sending means is provided an electric pulse to send out ultrasonic wave signals at different times with respect to each other and in order. Then, the ultrasonic wave signals are sent out from the transducer and are propagated in a medium, on which the transducer is attached, with a predetermined refraction angle corresponding to the time interval of the application of the electric pulse between adjacent sending means. Ultrasonic wave signals which are reflected at interval defects or at a bottom surface of the medium are received by each of a plurality of receiving means which generate electric signals corresponding to the received ultrasonic wave signals. The electric signals generated by the plurality of receiving signals are added with a time interval, which is identical with that of the sending out of the ultrasonic wave signals. By the method, the ultrasonic wave signals are propagated with a predetermined refraction angle or are focused to a predetermined position corresponding to the time interval. However, it is needed to adjust each time interval between the plurality of sending means precisely. If it is embodied by some electrical delay circuits, the circuit will be very large in volume and very expensive. If it is embodied by some computer, it will be very expensive too.